The present invention is directed to a system and method for reducing the cumulative noise resulting from the uplink stages connected to a plurality of remote antenna units in a distributed antenna network. More particularly, the present invention reduces the cumulative noise by utilizing a signal strength processor.
As personal communications services (PCS) evolve as the next generation of cellular telephone technology, systems and techniques for simply and efficiently transmitting and receiving communication signals are being investigated. One known system is a distributed antenna network (which is also referred to as a multicast network) which provides coverage over substantial areas by a plurality of remote antenna units. An example of a distributed antenna network is illustrated in FIG. 1 where an individual transceiver unit 10 is connected to a plurality of cells 20.sub.1, . . . 20.sub.n by transmission media 30 which transports radio signals between the transceiver unit 10 and the cells 20.sub.1, . . . 20.sub.n. Each of the cells 20.sub.1, . . . 20.sub.n include remote antenna units 21.sub.1, . . . 21.sub.n. The remote active antenna units 21.sub.1, . . . 21.sub.n may be connected to the transmission media 30 by frequency converting circuitry 22.sub.1, . . . 22.sub.n for certain applications.
Various infrastructures are being developed and modifications of existing infrastructures are of great interest as an alternative for PCS because they are fully capable of providing high quality signals at lower costs than traditional cellular infrastructures. For example, CATV infrastructures have been modified for use in PCS. Such modifications include the CATV infrastructures using a hybrid fiber/coax (HFC) cable infrastructure to increase capacity and improve service quality. Although it is theoretically possible for any CATV infrastructure to support PCS with the proper modifications, the HFC cable infrastructure offers an attractive option as an economical alternative to wireless providers seeking to avoid the high cost of network construction.
FIG. 2 illustrates the basic components of a CATV infrastructure used to support PCS. In FIG. 2, base station equipments 50.sub.1 and 50.sub.2 are connected to a public network, such as a public switched telephone network. Remote antenna signal processors (RASPs) 52.sub.1 and 52.sub.2 connect the base station equipments 50.sub.1 and 50.sub.2 to a fiber equipment 54. The fiber equipment 54 is connected to a fiber node 58 by fiber optic cable 56 and the fiber node 58 is connected to remote antenna driver (RAD) nodes 62.sub.1 and 62.sub.2 by two-way coaxial cable 60. The RAD nodes 62.sub.1 and 62.sub.2 each include a group of RADs 64.sub.1 and 64.sub.2 and 66.sub.1 and 66.sub.2 respectively connected to antennas 68.sub.1, 68.sub.2, 70.sub.1, and 70.sub.2. This CATV infrastructure converts radio frequency signals into CATV frequency signals usable in the existing CATV infrastructure and converts the CATV frequency signals back into radio frequency signals for broadcast. More specifically, the RASPs 52.sub.1 and 52.sub.2 convert the radio frequency signals from the base station equipments 50.sub.1 and 50.sub.2 and then send the converted signals in the downlink path toward the appropriate fiber node 58 and onto the coaxial cable 60.
The RADs 64.sub.1, 64.sub.2, 66.sub.1, and 66.sub.2 are connected to the coaxial cable 60 for converting CATV frequency signals into assigned radio frequency signals. Radio frequency signals may be received by the RADs 64.sub.1, 64.sub.2, 66.sub.1, and 66.sub.2 which convert these signals into signals of frequencies suitable for transmission in the uplink path of the CATV infrastructure. Thereafter, the RASPs 52.sub.1 and 52.sub.2 convert the upstream CATV frequency signals back into radio frequency signals for processing by the base station equipments 50.sub.1 and 50.sub.2. This CATV infrastructure may also accommodate equipment for multiple modulation schemes, such as time division multiple access (TDMA), code division multiple access (CDMA), and frequency division multiple access (FDMA).
Radio telephony systems may utilize this CATV infrastructure by operating on available portions of the radio frequency spectrum over fiber optic and coaxial cables, which are widely available in urban areas, so that such systems may be installed to take advantage of this existing infrastructure. The large installed base of fiber optic and coaxial cables used by CATV operators may thereby be effectively exploited at a minimal cost by this infrastructure which distributes the signals to the appropriate antenna locations.
The antenna network used in CATV infrastructures is commonly termed a distributed antenna network or multicast network because coaxial or heliaxial cable is used to feed a plurality of antennas distributed within a coverage area. The use of multiple antennas effectively increases and controls the size of the coverage area. When used in a two-way communication system, a distributed antenna network suffers from some problems. Low power urban cellular base stations and low power PCS handsets of limited range may introduce noise to the network which limits the coverage area by the network.
Also, each remote antenna contributes noise that is relatively more important in the uplink. These noise problems significantly increase as the number of remote antennas in the-distributed antenna network increases. The cumulative noise is the sum of the individual noise contributions of the remote antennas. Thus, having numerous remote antennas can severely degrade the performance of a communication system in which the signal-to-noise ratio is a critical parameter.
As existing CATV networks continue to be modified for use in telephony communication, it is desirable to reduce noise generated in distributed antenna networks so that a system using many remote antennas is useful for telephony communication over large coverage areas.